Sharma, AchlaGudi, Santosh2024-01-042024-01-042023Gudi, Santosh (2023). Understanding the effect of combined drought and early heat stress in wheat (Triticum aestivum L.) (Unpublished Ph.D. Dissertation). Punjab Agricultural University, Ludhiana, Punjab, India.https://krishikosh.egranth.ac.in/handle/1/5810205635Wheat is an important cereal crop constrained by several abiotic stresses, including heat and drought. Heat and drought can occur either independently or together, and in either case, they significantly affect wheat productivity. The present investigation was carried out to understand the effect of heat and drought stress on agronomic, physiological, and grain quality parameters in the wheat core-set consisting of 198 germplasm lines. Huge genetic variation for the studied traits under all the environmental conditions was observed. Late sowing reduced grain yield by 45.9 and 67.3 percent, respectively, during 2020-21 and 2021-22. Combined heat and drought stresses had a more severe effect on seedling characteristics than the individual stresses. Late sowing significantly increased the phenol reaction score, grain hardness, grain protein content (GPC), and grain moisture, whereas it reduced the grain appearance score, hectoliter weight (HW), and solvent retention capacity (SRC). Grain quality parameters are significantly reduced in modern cultivars as compared to land races or old varieties. Genome-wide association study (GWAS) using 12,511 single nucleotide polymorphisms (SNPs) identified total 204 QTNs for agronomic traits, of which 25 were high-confidence MTAs, 205 for chlorophyll fluorescence parameters, of which 11 were high-confidence MTAs, 25 for seedling vigour, of which 3 were high-confidence MTAs, 27 for coleoptile length, of which 7 were high-confidence MTAs, 4 for grain hardness, of which one was high-confidence MTA, 13 for HW, of which 3 were high-confidence MTAs, 13 for GPC, of which 5 were high-confidence MTAs, 4 for sedimentation volume, of which 3 were high-confidence MTAs, and 55 for SRC, of which 17 were high-confidence MTAs. The "field-based speed breeding" protocol developed in-house aids in achieving F5 generation in two years. Drought and heat-tolerant genotypes (viz., BWL-7504 and PN-317) identified in this study may become the starting material for breeding stress-resilient cultivars. High-confidence QTNs identified from this study may become the basis for marker-assisted breeding of heat and drought resilient wheat cultivars. The advanced breeding lines (F5 generation) with enhanced heat and drought tolerance identified in this study can be evaluated in multi-locational trials before being released as a new variety.EnglishThesis